1. Field of the Invention
The present invention relates to a broadband antenna, and more particularly, to an antenna having broadband characteristics in a low frequency band.
2. Description of the Related Art
Recently, mobile communication terminals are diversified in the frequency ranges with advancement in wireless communication technology. In particular, the frequency bands currently used in the wireless communication include: 800 MHz to 2 GHz for global system for mobile communication (GSM) and code division multiple access (CDMA) mobile phones; 2.4 GHz and 5 GHz for wireless local area network (WLAN); 13.56 MHz, 433.92 MHz, 908 to 914 MHz, 2.45 GHz for non-contact radio frequency identification (RFID); 2.4 GHz band for Bluetooth; 1.575 GHz for global positioning system (GPS); 88 to 108 MHz for FM radio; 475 to 750 MHz for digital video broadcasting-handheld (DVB-H); and 175 to 225 MHz for ground wave digital multimedia broadcasting (DMB), ultra wide band (UWB) and Zigbee.
In general, it is possible to manufacture and mount a small-sized antenna, having a frequency range of 1 GHz or higher, in a mobile communication terminal by typical design technology. However, a VHF antenna of a low frequency range (e.g. hundreds of MHz band), in particular, an antenna for ground wave DMB requires tens of centimeters of length for ensuring a resonant frequency, and thus is not suitable to be mounted in the mobile communication terminal.
The broadband antennas currently under development include a horn antenna and a log periodic antenna, which however are not small enough to be mounted internally and have high directivity, thus not suitable for mobile communication terminals such as mobile phones. Other broadband antennas having omni-directional radiation characteristics while having a small size include a slot antenna, a meander line antenna, a spiral antenna, a loop antenna and the like. However, there does not exist a small (e.g. about 1 cm3) antenna capable of covering a broad band of 475 to 750 MHz to date.
Further, there is no single built-in antenna, which can realize both T-DMB (174 to 216 MHz) and DVB-H (475 to 750 MHz) to date.